a(n) = A064842(n)/2.

Terms

a(0) =0a(1) =1a(2) =3a(3) =9a(4) =18a(5) =33a(6) =53a(7) =81a(8) =116a(9) =161a(10) =215a(11) =281a(12) =358a(13) =449a(14) =553a(15) =673a(16) =808a(17) =961a(18) =1131a(19) =1321a(20) =1530a(21) =1761a(22) =2013a(23) =2289a(24) =2588a(25) =2913a(26) =3263a(27) =3641a(28) =4046a(29) =4481